The present invention relates to pistons for internal combustion engines and particularly to pistons having insulated crowns for use in compression ignition engines.
Piston crowns having insulation to increase the operating temperature of the combustion chamber are well known. In most of the pistons shown in the prior art, however, the level of insulation is very high, usually seeking a temperature increase sometimes as high as 100%.
Although large temperature increases may be beneficial in terms of fuel efficiency it is now being realized that lower temperature increases are more beneficial in some respects. For example, it has been found that particulate emissions are significantly less at lower temperature increases. The reduction in particulate emissions at a crown surface temperature increase in the region of only 5% to 15% may be sufficient to allow the elimination of a very costly particulate trap from the engine exhaust system.